A multimodal investigation of perceptual awareness in Alzheimer’s disease

Understanding how the contents of consciousness, particularly perceptual awareness, change with the progression of AD is crucial for meaningful person-centred care. This is especially important in severe AD when impairments in language and other cognitive domains limit reporting of experience.

We investigated whether electrophysiological (EEG) and fMRI signatures of perceptual awareness remain present in people with mild-moderate and severe AD. A visual masking paradigm examined visual awareness negativity (VAN) and late positive (LP) electrophysiological responses and activation in visual cortex and fronto-parietal regions; and a complex audio-visual (movie) task examined activation in fronto-parietal networks previously associated with perceptual awareness.

Healthy older controls demonstrated cortical responses characteristic of awareness in both EEG and fMRI modalities. In people with mild-moderate AD, VAN and LP markers and fronto-parietal activation were significantly reduced. In participants with severe AD, who were behaviourally minimally responsive, there was limited evidence of frontoparietal markers of perceptual awareness, however this may reflect attentional and task insensitivity.

These results demonstrate that the brain mechanisms associated with perceptual awareness become increasingly impaired with progression of AD. This motivates further investigation into the dimensions of awareness affected by the disorder with implications for treatment and management of people with dementia.